In HSDPA (High Speed Data Packet Access), where many users utilize physical resources on a specific shared channel, a packet scheduler is needed for scheduling the packets at given time instants, or transmission opportunities. The task of the scheduler is to select a user or a plurality of users that shall be allowed for having a transmission performed during a certain transmission time interval (TTI). In a cellular system, data queues pertaining to individual users are consecutively evaluated. Various selections shall be done at every scheduling instant, e.g. at every sub-frame for HSDPA, and according to a certain scheduling strategy.
Packet schedulers and scheduling strategies for HSDPA are widely known in the art. For HSDPA, the packet scheduler is located in the MAC-hs sub layer of layer 2, on the UT-RAN side. This is standardized according to 3GPP TS 25.321, Medium Access Control (MAC) protocol specification, c.f. FIG. 1.
FIG. 1 shows different entities required for the traffic data handling in the MAC-hs layer. A user given access to the HSDPA service comprises a number of MAC-d flows, sent on the Iub interface, each one containing packets of one or several priorities. These packets are buffered in MAC-hs in different priority queues via the priority queue distribution entity. Furthermore, as can be seen, there exists a scheduling/priority handling routine that considers all priority queues and selects which one shall transmit for each transmission opportunity. The priority queue selected for transmission is allocated resources in the so called HARQ (Hybrid Automatic repeat Request) entity, where the scheduled packet is stored for transmission and possibly one or more retransmissions. Finally there is a TFRC (Transport Format and Resource Combination) selection routine running that decides, for each transmitted package how much physical resources shall be allocated in terms of transmission power (W), number of HS-PDSCH codes and modulation (QPSK/16QAM (Quadrature Phase Shift Keying/16 Quadrature Amplitude Modulation)).
In FIG. 2, a known network is shown comprising a content server, a core network (CN), a radio network controller (RNC), a radio base station (RBS) and a plurality of user entities (UE1 . . . UEn). Downlink Traffic data pertaining to each user entity is transmitted through the RNC and further on to the RBS, whereby data is buffered in queues residing in the RNC, index QN, respectively and in the RBS, index QB, respectively.
Prior art document WO2005/034418 shows a medium access control (MAC) priority queue based scheduling pertaining to HSDPA. The scheduling unit is based on hybrid automatic repeat request (HARQ) entity and a TFRC entity.
Each user entity may require various scheduling priorities for various data streams, depending on the service. Voice over IP may e.g. require 2 scheduling priorities, while web surfing only a single scheduling priority reflecting the best effort nature of the service. For this reason, a number of specific queues are set up in both the RNC and the RBS, pertaining to a given user entity and data stream. By way of example, data queue QB(1, 2) corresponds to packets for user entity UE1, second scheduling priority.
Data pertaining to each user entity is transmitted from the content server over the core network, further on over the Iu Interface to the RNC where various data corresponding to various respective data streams are stored in priority queues. The data of queues in the RNC in FIG. 2 may be identified by QN(UE, DS), where UE is the user entity number and DS is the identifier for the particular data stream. Since a service typically consists of several parallel data streams, there may be several priority queues for a given user entity, or there may be only one queue of traffic data, in the RNC or in the RBS respectively. The priority queues may contain one or more packets or no packets at all. However, once a user is allocated to the HSPDA service of the network, data could be expected for that particular user.
In known solutions, all priority queues of all users are considered for transmission in a scheduler in each sub-frame. Thus, in the hardware implementation, for each priority queue that is allowed, the HSDPA service in a cell demands a certain amount of clock cycle capacity and memory consumption. This puts a fundamental limit on scheduler capacity.